Vent valve

ABSTRACT

A vent valve for an air braking system of a vehicle comprises an elastomeric valve member ( 11 ) held in relation to a vent ( 17 ) and having a restricted vent passageway. A continuous depending rib ( 23 ) is engageable with a valve seat ( 28 ) to close the vent passageway as increasing pressure acts on the head ( 21 ) of the valve member ( 11 ). The valve member ( 11 ) permits a fluid chamber to be connected to exhaust until pressure in the chamber reaches a predetermined level.

This invention relates to a vent valve for an air braking system of avehicle.

Vent valves are required in an air braking system in order to drainmoisture which may accumulate in the signal or supply lines. Manuallyoperable valves are somewhat difficult to design, and are generallyundesirable because they tend to be opened at rather infrequentintervals. Automatic vent valves are therefore preferred, hitherto suchautomatic valves have included precision engineered components such aspistons, springs and valve seating devices, and are therefore somewhatexpensive.

An air braking system of a vehicle also includes a compressor which isbrought on-load by a demand signal. When the compressor is off-load, butrunning, lubrication oil may accumulate on the head of the piston. Thisoil will enter the air braking system when the compressor is broughton-load, and it has been proposed to vent such oil laden air to exhaust.Again, the vent valve proposed for this purpose is a precisionengineered component which is rather expensive.

What is required is an inexpensive and adaptable valve to suit either orboth of the aforementioned circumstances.

According to the invention there is provided a vent valve for a fluidpressure circuit, the valve comprising a closed chamber having an inletport and a vent, the vent defining a valve seat about the inner sidethereof and having a resilient valve member engageable with said seat,the valve member comprising a head, a continuous rib depending from saidhead and adapted for sealing engagement with said seat, and means tohold said valve member adjacent said vent; the rim of said head engagingsaid chamber about said seat to resiliently support said rib away fromsaid seat, and defining openings whereby said chamber can communicatewith said vent; the vent valve thereby defining a fluid passage fromsaid chamber via said openings, seat and vent, and said fluid passagehaving a restricted flow area such that increasing pressure in saidchamber deforms said head towards said vent, thereby sealingly engagingsaid rib and seat.

Such a valve can be very simply constructed using a unitary moulding ofe.g. synthetic rubber. The valve preferably incorporates retaining meansto secure the valve member in relation to the vent, these retainingmeans preferably being provided on the valve member itself. Theretaining means may for example be a snap fit projection of the valvemember, and in the preferred embodiment comprise a limb removablyengageable in the vent itself.

The valve seat and depending rib are preferably circular, the seat beingplanar and immediately adjacent the vent.

The vent may include a passage having inwardly directed arms definingvent passageways therebetween. The vent may be defined by an annularinsert, and such an arrangement permits variation of the area of saidvent passageways.

Preferably the depending rib defines with the valve seat a travel stopfor the valve member, thereby restricting the stroke of the valve fromthe rest condition.

The valve is particularly useful in an air braking system of a vehicle,and may be used to vent part of the system automatically. In a preferredembodiment the valve is positioned in the signal line from the governorvalve to the compressor, and purges accumulated moisture from this line.

Other features of the invention will be apparent from the followingdescription of a preferred embodiment in which:

FIG. 1 is an axial section through a valve member according to theinvention,

FIG. 2 is a transverse section on line 2—2 of FIG. 1, and

FIG. 3 is an isometric view of the valve member of FIG. 1 from above andto one side.

With reference to the drawings, there is illustrated a vent valve 10comprising an elastomeric valve member 11 situated in a schematichousing 12 having a chamber 13 with an inlet 14 from a source S and anoutlet 15 to a consumer C. The chamber also has a plurality of ventpassages 17 communicating to the exterior of the housing and defined bya plurality of equispaced inwardly directed arms 18.

The elastomeric valve member 11 is of resilient material having astiffness appropriate for the purpose, as will be further explainedbelow. It comprises a circular dome-like head 21 having a plurality ofequispaced peripheral passages 22 in order to permit communication fromthe exterior of the dome to the interior, and vice versa. A continuouscoaxial depending rib 23 is provided on the underside of the dome. Theregions between each passage 22 constitute supporting legs 24, and thewhole, as shown in FIG. 3, has the appearance of the Millennium Dome. Inthe rest position, the legs 24 depend to a greater extent than the rib23.

The valve member 11 has a depending coaxial limb 25 within the rib 23which projects beyond the legs 24. The terminal end of the limb 25 has aradially outwardly extending shoulder 26 which in use engages theunderside of the arms 18, as illustrated, so as to retain the valvemember 11 in the housing 12. The terminal end of the limb 25 has aninternal blind recess 27 in the centre to permit flexibility of theshoulder 26, for installation purposes.

In the rest condition, illustrated in FIG. 1, the axial length of thearms 18 is determined such that the valve member is installed underslight tension with the shoulder 26 and legs 24 firmly engaged with thehousing 12. The rib 23 is spaced above the housing 12, as shown, so asto define a fluid passageway from the chamber 13 to the exterior of thevalve housing 12 via the passages 22,17.

Although not illustrated, the housing 12 would be manufactured in such away that the valve member can be pressed past the arms 18 from above.

Operation of the vent valve is as follows. As noted above the chamber 13is vented to the exterior when the valve member 11 is in the restcondition.

If fluid under pressure is supplied from the source S, pressure inchamber 13 will increase. At first the passages 22,17 will permitchamber pressure to vent, but as pressure continues to increase theforce acting on head 21 will increase whilst at the same time the flowthrough passages 22,17 will be restricted. Finally the head 21 willdeform downwardly (as viewed) under pressure, bringing the rib 23 intocontact with a seat 28 of the housing 12, and closing the vent. Thevalve member will remain in the seated condition until the pressure inchamber 13 has fallen to an extent sufficient to allow the inherentresilience of legs 24 to force the head 21 upwards, thus re-opening thevent via passages 17.

The closing and opening pressures of the valve 10 are dependent on anumber of factors, including the stiffness of the valve material, thesize of the vent passages 22,17, and the rate of pressure increase inthe chamber 13. The skilled man will make adjustments in order to obtaina valve which will meet the desired performance criteria.

The depending rib 23 has the particular advantage of limiting the strokeof the head 21, in addition to providing a sealing surface. The rib 23may also define the minimum flow area through the valve, if desired.

The vent valve described herein will close a short time after acompressor, as source S, has been brought off-load by a rise in pressurein a signal line from the usual governor valve. If placed low down in asignal line, the chamber 13 will act as a sump for moisture, and thevalve member 11 will permit such moisture to be dynamically blown to theexterior as the valve moves from the open to the closed condition.Likewise, oil laden air or moisture from an idling compressor can bevented by a similar valve as the compressor is brought on-load, thuspreventing such air reaching the consumer, and in particular a desiccantfilled air dryer of a braking system.

The valve 10 has been described with an inlet port 14 and an outlet port15. However the valve will work equally well if an inlet port only isprovided, connection from the source to the consumer being establishedoutside the chamber 13.

The valve member 11 may be retained in any convenient manner, andincorporated in any fluid device having a vent opening.

What is claimed is:
 1. A vent valve for a fluid pressure circuit, thevalve comprising a closed chamber having an inlet port and a vent, thevent defining a valve seat about the inner side thereof and having aresilient valve member engageable with said seat, the valve membercomprising a head, a continuous rib depending from said head and adaptedfor sealing engagement with said seat, and means to hold said valvemember adjacent said vent; the rim of said head engaging said chamberabout said seat to resiliently support said rib away from said seat, anddefining openings whereby said chamber can communicate with said vent;the vent valve thereby defining a fluid passage from said chamber viasaid openings seat and vent, and said fluid passage having a restrictedflow area such that increasing pressure in said chamber deforms saidhead towards said vent, thereby sealingly engaging said rib and seat. 2.A vent valve according to claim 1 and further comprising retaining meansto secure the valve member in relation to the vent.
 3. A vent valveaccording to claim 2 wherein said retaining means are provided on thevalve member.
 4. A vent valve according to claim 3 wherein saidretaining means comprises a snap fit projection of the valve member. 5.A vent valve according to claim 4 wherein said retaining means comprisesa limb removably engageable in said vent.
 6. A vent valve according toclaim 1 wherein said valve seat and depending rib are circular.
 7. Avent valve according to claim 1 wherein said seat is planar.
 8. A ventvalve according to claim 1 wherein said vent includes a passage havinginwardly directed arms defining vent passageways therebetween.
 9. A ventvalve according to claim 1 wherein said vent comprises an annular insertof said chamber.
 10. A vent valve according to claim 1 wherein saiddepending rib and valve seat co-operate to define a travel stop forlimiting resilient deformation of said valve member.
 11. A vent valveaccording to claim 6 wherein said depending rib and valve seat cooperateto define a travel stop for limiting resilient deformation of said valvemember.